From: Russ Cox <rsc@golang.org>
Date: Tue, 1 Dec 2020 17:02:16 +0000 (-0500)
Subject: [dev.regabi] cmd/compile: handle OCONVNOP better in ssa
X-Git-Tag: go1.17beta1~1539^2~387
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=59b8916d482bdca933885881dff54365432ec9f5;p=gostls13.git

[dev.regabi] cmd/compile: handle OCONVNOP better in ssa

This CL improves handling of OCONVNOP nodes during ssa generation,
so it is not toolstash safe.

An OCONVNOP wrapper is necessary for the "for" condition of
certain compiled range loops, and the boolean evaluator was
not looking through them properly, generating unnecessary
temporaries. That change saved 8k of the (13 MB) go binary.

The other changes just streamline the handling of OCONVNOP
to be more like what OSTMTEXPR will be like. They have no
effect on output size but do tweak the ssa graph a little, which
causes different register decisions and therefore different output.

Change-Id: I9e1dcd413b60944e21554c3e3f2bdc9adcee7634
Reviewed-on: https://go-review.googlesource.com/c/go/+/274598
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
---

diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 7c74054b60..d53bd1aa4f 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -2103,6 +2103,9 @@ func (s *state) expr(n ir.Node) *ssa.Value {
 		// Assume everything will work out, so set up our return value.
 		// Anything interesting that happens from here is a fatal.
 		x := s.expr(n.Left())
+		if to == from {
+			return x
+		}
 
 		// Special case for not confusing GC and liveness.
 		// We don't want pointers accidentally classified
@@ -2966,6 +2969,10 @@ func (s *state) condBranch(cond ir.Node, yes, no *ssa.Block, likely int8) {
 		s.stmtList(cond.Init())
 		s.condBranch(cond.Left(), no, yes, -likely)
 		return
+	case ir.OCONVNOP:
+		s.stmtList(cond.Init())
+		s.condBranch(cond.Left(), yes, no, likely)
+		return
 	}
 	c := s.expr(cond)
 	b := s.endBlock()
@@ -4903,6 +4910,9 @@ func (s *state) addr(n ir.Node) *ssa.Value {
 		return s.newValue1I(ssa.OpOffPtr, t, n.Offset(),
 			s.entryNewValue0(ssa.OpGetClosurePtr, s.f.Config.Types.BytePtr))
 	case ir.OCONVNOP:
+		if n.Type() == n.Left().Type() {
+			return s.addr(n.Left())
+		}
 		addr := s.addr(n.Left())
 		return s.newValue1(ssa.OpCopy, t, addr) // ensure that addr has the right type
 	case ir.OCALLFUNC, ir.OCALLINTER, ir.OCALLMETH:
diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go
index f439237936..c0f447f1a2 100644
--- a/src/cmd/compile/internal/gc/walk.go
+++ b/src/cmd/compile/internal/gc/walk.go
@@ -966,6 +966,9 @@ opswitch:
 
 	case ir.OCONV, ir.OCONVNOP:
 		n.SetLeft(walkexpr(n.Left(), init))
+		if n.Op() == ir.OCONVNOP && n.Type() == n.Left().Type() {
+			return n.Left()
+		}
 		if n.Op() == ir.OCONVNOP && checkPtr(Curfn, 1) {
 			if n.Type().IsPtr() && n.Left().Type().IsUnsafePtr() { // unsafe.Pointer to *T
 				n = walkCheckPtrAlignment(n, init, nil)